Method of producing a proximal connector end of an implantable lead

ABSTRACT

A connector for an implantable medical lead that is electrically and mechanically connectable to an implantable medical device, has a connector pin made of a first conducting material. A tubular insulator made of an insulating material concentrically surrounds at least a portion of the pin. A connector ring made of a second conducting material is concentrically positioned around at least a portion of the insulator. The insulator is connected to the connector ring by spark plasma sintering in the case of an active fixation lead, and is connected to the ring and the pin by spark plasma sintering in the case of a passive fixation lead.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to implantable leads, and inparticular to proximal end portions for such implantable leads.

2. Description of the Prior Art

Body implantable electrical leads form the electrical connection betweenan implantable medical device (IMD), such as cardiac pacemaker, cardiacdefibrillator or cardioverter, and body tissue, such as the heart, whichis to be electrically stimulated. As is well known, the leads connectingthe IMD with the tissue may be used for pacing/defibrillation and forsensing electrical signals produced by the tissue.

The implantable leads of today are complex arrangements, generallyincluding multiple different lead elements of different materials andtherefore having different characteristics. In particular, connectorarrangements or proximal end portions of implantable leads are complexarrangements, generally consisting of a multitude of different leadelements that have to be interconnected to form the final connector.This assembling process is complex and time-consuming having multipleseparate sub-assembly steps.

SUMMARY OF THE INVENTION

There is therefore a need for a lead manufacturing process that allowsassembling of proximal lead end portions using few including elementsand in few assembly steps. The present invention overcomes these andother drawbacks of the prior art arrangements.

It is a general object of the present invention to provide a leadconnector comprising mechanically inter-connected connector elements ofdifferent materials.

It is another object of the invention to provide a connector arrangementthat can be simply handled in the manufacture of lead connectors forimplantable medical leads.

Briefly, the present invention involves a connector assembly of animplantable medical lead for providing a mechanical and electricalconnection to an implantable medical device.

The connector assembly has a central connector pin made of a firstconducting material, such as stainless steel. In a first embodimentadapted for active fixation implantable leads, at least a portion of theouter lateral pin surface is coated with a protective layer. A tubularinsulator is concentrically provided around at least a portion of thecoated pin. The insulator is made of an electrically insulatingmaterial, such as a ceramic. A connector ring made of a secondconducting material, such as stainless steel, is concentrically providedaround at least a portion of the outer lateral insulator surface.According to the present invention, spark plasma sintering is applied tothe assembly for mechanically connecting the connector ring to thetubular insulator. The protective layer prevents the insulator frommechanically bonding to the connector pin. After removal of theprotective layer, a spacing is formed between the outer pin surface andthe inner insulator surface. As a consequence, the connector pin isrotatable relatively the mechanically inter-connected sub-assemblyconsisting of the insulator and the ring electrode. However, due to thedesign of the pin, i.e. having a waist surrounded by proximal and distallead portions with comparatively larger diameters, the sub-assembly islongitudinally restricted relative the connector pin by these proximaland distal pin portions.

A connector assembly adapted for a passive fixation implantable leaddoes not have any protective coating on the pin surface. As aconsequence, the tubular insulator becomes mechanically connected toboth the connector pin and the connector ring.

The invention offers the following advantages:

-   -   Requires fewer lead components for manufacturing a lead        connector assembly;    -   Allows reliable mechanical inter-connection of connector        elements of different materials;    -   Simplifies the assembly process;    -   Provides a rigid connector design; and    -   Same connector elements and similar manufacturing process can be        used for both passive and active fixation lead connectors.        Other advantages offered by the present invention will be        appreciated upon reading of the below description of the        embodiments of the invention.

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an implantable active fixation lead accordingto an embodiment of the present invention.

FIG. 2 is a side view of an implantable passive fixation lead accordingto an embodiment of the present invention.

FIG. 3 is a schematic overview of a subject having an implantablemedical device connected to an implantable lead according to anembodiment of the present invention.

FIG. 4 is an axial cross section view of the proximal end portion of animplantable passive fixation medical lead according to an embodiment ofthe present invention.

FIG. 5 is an axial cross section view of the proximal end portion of animplantable passive fixation medical lead according to FIG. 4 equippedwith an insulating seal.

FIG. 6 is an axial cross section view of the proximal end portion of animplantable active fixation medical lead according to an embodiment ofthe present invention.

FIG. 7 is an axial cross section view of the proximal end portion of animplantable active fixation medical lead according to FIG. 6, in whichthe protective coating has been removed.

FIG. 8 is an axial cross section view of the proximal end portion of animplantable active fixation medical lead according to FIG. 7 equippedwith an insulating seal.

FIG. 9 is a flow diagram illustrating a method of producing a proximalend portion of an implantable passive fixation lead according to anembodiment of the present invention.

FIG. 10 is a flow diagram illustrating a method of producing a proximalend portion of an implantable active fixation lead according to anembodiment of the present invention.

FIG. 11 is a schematic block diagram of a spark plasma sinteringapparatus that can be used according to the present invention.

FIGS. 12A and 12B are scanning electron microscope images of a Pt—A1₂O₃connection at 500× magnification (FIG. 12A) and 4000× magnification(FIG. 12B).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Throughout the drawings, the same reference characters will be used forcorresponding or similar elements.

The present invention relates to implantable medical leads or catheters,and in particular to a connector arrangement in the proximal end of suchleads. This connector arrangement of the invention is adapted forconnection to different implantable medical devices (IMDs), such aspacemakers, cardioverters, defibrillators and other implantableelectrical medical devices.

FIG. 1 is a schematic illustration of an implantable lead 100 accordingto an embodiment of the present invention. The lead 100 comprises a leadbody 130 extending a long a central, longitudinal axis. The lead 100 hasa proximal end 106 carrying a connector assembly 104 for electricallyconnecting the lead body 130 to an IMD. The lead 100 also has a distalend 102 comprising a header with electrodes 120, 140 and fixationelements 110. The lead 100 has non-limitedly been illustrated in theform of a so-called active fixation medical lead 100, implying that thefixation element 110 is in the form of a helical, screw-in fixationelement 110 adapted to be extended so as to project from the distal endof the header. The helical screw-in fixation element 110 is preferablyactive electrically so as to function as an electrode when implanted tostimulate selected tissue, such as cardiac tissue, and/or senseelectrical activity of the tissue. Consistent with teachings well knownin the art, one or more portions of such a helical electrode 110 may beelectrically insulated along its length. The helical electrode 110 notonly has a stimulating and/or sensing function but also serves to anchoror stabilize the distal lead portion 102 relative to the tissue.

The distal lead portion 102 also has a ring electrode 140 or indifferentelectrode for electrically stimulating adjacent tissue and/or forsensing electrical activity of tissue. An optional tip electrode 120 maybe provided at the most distal end 102 of the lead 100 as is well knownin the art. The tip electrode 120 may optionally be made of a radiopaquematerial for facilitating monitoring implantation of the lead 100 into apatient body.

The connector assembly 104 at the proximal lead end 106 is adapted toelectrically and mechanically couple the lead body 130 to the IMD. Theassembly comprises terminal contacts in the form of a tubular, rotatablepin terminal contact 160, often denoted connector pin 160, and a ringterminal contact 150, generally referred to as connector ring 150. Thesetwo contacts 150, 160 are positioned to engage corresponding electricalterminals within a receptacle in the IMD. In order to prevent ingress ofbody fluid into the IMD receptacle, the connector assembly may beprovided with spaced-apart sets of seals 170, 171, well known in theart.

FIG. 2 is an illustration of another embodiment of a lead 200 to whichthe teachings of the present invention can be applied. This lead 200 isa so called passive fixation lead, where the helical screw-in fixationelement has been replaced by, for instance a collar, fines or, as in thefigure, tines 210 for anchoring the lead body 230 to a selected tissue.

The passive fixation lead 200 has a distal end 202 with an optional,preferably radiopaque, tip electrode 220 and a ring electrode 240. Theproximal lead end 206 has a connector assembly 204 according to thepresent invention with an electrically conducting connector pin 260 andconnector ring 250. These two terminals 250, 260 are adapted forconnection to matching electrical terminal in a receptacle of the IMD.The connector 204 preferably also comprises seal rings 270, 271 forpreventing body fluids from entering the IMD receptacle.

In clear contrast to the connector pin of the active fixation lead inFIG. 1, the connector pin 260 does not have to be rotatable relative thelead body 230 in this embodiment as no screwing fixation element ispresent.

FIG. 3 is a schematic overview of a subject 1 equipped with an IMD 300connected to the subject's heart 10. The IMD 300 is illustrated as adevice that monitors and/or provides therapy to the heart 10 of thepatient 1, such as a pacemaker, defibrillator or cardioverter. However,the present invention is not limited to cardiac-associated IMDs but mayalso be practiced with other implantable medical devices, such as drugpumps, neurological stimulators, physical signal recorders, oxygensensors, or the like, as long as the IMD 300 is equipped with or isconnected to at least one medical lead 100, 200 according to the presentinvention.

The IMD 300 can wirelessly communicate with an external device 400,non-limitedly illustrated as a programmer 400 in the figure. Theexternal device 400 could alternatively be a physician's workstation, ahome monitoring device or actually any data processing unit havingcapability of receiving data collected by the IMD 300 and preferablysending instructions and commands to the IMD 300. The external device400 is preferably connected to a display screen 410 allowing display ofthe collected diagnostic parameters and data.

The present invention provides a novel bonding technique used formechanically connecting connector elements of different material toobtain a robust and reliable mechanical connection. Traditionally, amultitude of different connecting techniques have been used in the art,including snap-fit solutions, adhesions, welds, etc. These knownconnecting techniques have pros and cons. A general problem is that theassembly generally becomes time-consuming and complex, as an operatorhas to simultaneously handle multiple separate lead components that areto be inter-connected. Furthermore, the number of connecting techniquesin the prior art of implantable lead assembly when connecting conductingmetal-based lead elements with non-conducting non-metal elements hasbeen rather limited. Generally, one may be limited to using differentadhesions and like, making the assembly processes complex andtime-consuming.

The present invention takes a radically different approach by utilizingspark plasma sintering for mechanically inter-connecting differentconnector elements to achieve a highly robust, reliable and corrosion-and strain-resisting connection. The spark plasma sintering techniquehas the further advantage in not being limited to be applied to metaland metal-based materials but can also be used for inter-connecting aconducting element, such as made of metal (alloy) material, to anon-conducting element, for instance made of a ceramic material.

FIG. 4 is a cross-sectional view of a proximal connector end 204 of apassive fixation implantable lead according to the present invention.The connector assembly 204 comprises a connector pin 260 made of a firstconducting material. This material is selected from the group includingmetals, such as platinum, titanium, tantalum, iridium and niobium, anddifferent alloys thereof, such as titanium alloys or platinum/iridium(Pt/Ir) alloys, including Pt/Ir 90/10 or Pt/Ir 80/20. Also other metalalloy materials can be used, including nickel-cobalt-chromium-molybdenumalloys, such as MP35N® (trademark of SPS Technologies, Inc.) or 35N LT®(trademark of Fort Wayne Metals Research Products Corp.), oriron-nickel-cobalt alloys, such as Kovar® (trademark of CarpenterTechnology Corp.). Further suitable materials include stainless steel,preferably stainless steel of medical grade, such as medical grade 316Lstainless steel.

The proximal end portion 262 of the connector pin 260 is adapted forelectrical connection to a mating terminal at a receptacle of the IMD.The distal end portion 264 of the pin 260 is adapted for connection toan inner conductor coil that runs through the length of the lead bodyfor connection with one of the electrodes (tip or ring electrode) at thelead header.

The connector pin 260 has a longitudinally running bore 266 throughwhich a stylet or guide wire can be inserted through the bore 266 of thepin 260 and into a longitudinal passageway within the lead body for thepurpose of delivering and steering the distal portion of the lead duringimplantation.

A tubular insulator 280 made of an insulating material is concentricallypositioned around a portion 268 of the connector pin 260. The insulator280 is, in this embodiment of the invention, mechanically connected tothe pin 260 by spark plasma sintering. Thus, an inner surface of theinsulator 280 is at least partly connected to the lateral surface of aportion 268 of the connector pin 260. The insulator 280 preferablycovers an intermediate portion 268 of the pin lateral surface betweenthe proximal end 262 for electrical connection to an IMD terminal andthe distal end 264 for mechanical and electrical connection to the innerconductor coil. In a preferred embodiment, the covered pin portion 268presents a smaller outer diameter as compared to the end portions 262,264. As a consequence, tubular insulator 280 can be formed and connectedto the pin 260 in a waist of the connector pin 260.

The tubular insulator 280 is made of an insulating material that can bespark plasma sintered to the conducting material of the connector pint260. Preferred such insulating materials include ceramic materials,including aluminium oxide (A1₂0₃), zirconium dioxide (ZrO₂) andpotassium sodium niobate (KNN) ceramics (K_(x)Na_(y)NbO₃). Otherpossible insulating materials include hydroxylapatite (Ca₅(PO₄)₃(OH)),magnesium oxide (MgO) and silicon dioxide (SiO₂). Also mixtures of anycombination of at least two of the above-mentioned insulating materialscan be used according to the invention.

The connector assembly 204 also comprises a connector ring 250 made of asecond conducting material concentrically positioned around at least aportion 282 of the tubular insulator 280. The connector ring 250 isadapted for electrical connection to an electrode terminal in the IMDreceptacle. A distal end of the connector ring 250 is adapted formechanical and electrical connection to an outer conductor coil thatwill run through the length of the lead body and end at the ringelectrode or tip electrode in the lead header.

The connector ring 250 is mechanically connected to the tubularinsulator 280 by spark plasma sintering to achieve a reliable and robustconnection even though the two connector elements are made of differentmaterials. The tubular insulator 280 electrically separates the twoconducting elements 250, 260 and therefore effectively functions as aninsulator therebetween.

The connector ring 250 preferably only covers a sub-portion 282 of thelateral surface of the insulator 280. As a consequence, a remainingportion 284 is bare and may be covered by a seal 270, which isillustrated in FIG. 5. The seal 270, which may be of silicone rubber,polyurethane, a Elast-Eon® polymer (trademark of Aor Tech International,a polymer of silicone with polyurethane), such as Elast-Eon® 2A, 2D, 3A,3LH or HF, or like, is preferably attached to the surface of remaininginsulator portion 284 and the proximal end surface 252 of the connectorring 250 utilizing a medical glue or adhesive.

The second conducting material of the connector ring 250 may be selectedfrom the group including metals, such as platinum, titanium, tantalum,iridium and niobium, and different alloys thereof, such as titaniumalloys or platinum/iridium (Pt/Ir) alloys, including Pt/Ir 90/10 orPt/Ir 80/20. Also other metal alloy materials can be used including anickel-cobalt-chromium-molybdenum alloy, such as MP35N® (trademark ofSPS Technologies, Inc.) or 35N LT® (trademark of Fort Wayne MetalsResearch Products Corp.), or an iron=nickel-cobalt alloy, such as Kovar®(trademark of Carpenter Technology Corp.). Further suitable materialsinclude stainless steel, preferably stainless steel of medical grade,such as medical grade 316L stainless steel. The ring 250 canadvantageously be made of the same conducting material as the connectorpin 260.

In this embodiment, the connector ring 250, tubular insulator 280 andconnector pin 260 are mechanically interconnected by spark plasmasintering to form a connector assembly 204. Thus, spark plasma sinteringis used for connecting an outer surface of a portion 268 of theconnector pin 260 to an inner surface of the insulator 280 and forconnecting an outer surface of a portion 282 of the insulator 280 to aninner surface of the connector ring 250. The connector assembly 204 canthen be handled as a single unit during the remaining lead assemblingprocess, which thereby significantly reduces the complexity and time ofthe lead manufacturing.

In the above-described connector embodiment all the connector elementsare mechanically connected and thereby cannot be separately moved orrotated relative each other. Such connectors are useful for passivefixation leads in which there is no need for being able to extend orretract a helical screw-in fixation element at the distal lead end bymanipulating the proximal lead end.

A connector assembly 104 useful in active fixation leads is illustratedin FIGS. 6 to 8. The connector 104 includes the connector pin 160 madeof the first conducting material, preferably having a central bore orchannel 166. A proximal pin end 162 is adapted for connection to aterminal at the IMD receptacle with a distal pin end 164 is to bemechanically and electrically connected to the inner conductor coil ofthe lead, electrically inter-connecting the connector pin 160 to anelectrode, typically the helix electrode, at the lead header.

A tubular insulator 180 made of an insulating material is concentricallyprovided around a portion 168 of the connector pin 160. However, inclear contrast to the connector assembly illustrated in FIGS. 4 and 5,the insulator 180 does not become mechanically connected to theconnector pin 160 during the spark plasma sintering process in thisembodiment. The reason for this is that a protective layer 190 (see FIG.6) is coated on the lateral surface of at least a portion 168 of theconnector pin 160 before initiating the spark plasma process. Thecoating 190 is also applied to the end surfaces of the proximal pin 162and the distal pin end 164 facing each other. Alternatively, the wholeoutside surface of the connector pin 160 is coated with the protectivelayer 190. This protective layer 190 is then removed after theSPS-process to thereby create a gap 195 (see FIGS. 7 and 8) between thetubular insulator 180 and the pin 160. The usage of such a protectivelayer 190 means that the inner diameter of the insulator 180 is slightlylarger than the outer diameter of the insulated waist portion 168 of theconnector pin 160. As a consequence, the pin 160 is rotatable relativethe insulator 180 thereby forming a bearing.

The proximal 162 and distal 164 pin portions having larger outerdiameters than the intermediate insulated pin portion 168 prevents anysignificant longitudinal movement of the tubular insulator 180 relativethe connector pin 160. The insulator 180 is thereby longitudinallylimited in the pin waist. The pin end portions 162, 164 can therefore beregarded as radially protruding shoulders or flanges, which will limitany longitudinal movement of the insulator 180.

The connector ring 150 made of the second conducting material is thenconcentrically positioned around at least a portion 182 of the tubularinsulator 180. The ring 150 is furthermore mechanically connected to theinsulator 160 through spark plasma sintering. Thus, an inner surface ofthe connector ring 150 is mechanically connected to the lateral surfaceof at least a portion 182 of the insulator 180. As the connector ring150 becomes attached and anchored to the insulator 180, the connectorpin 180 is also rotatable relative the connector ring 150.

A remaining non-covered surface 184 of the tubular insulator 180 is thenpreferably covered by one or more seals 170 as is illustrated in FIG. 8.

FIG. 9 is a flow diagram illustrating a method of producing a proximalconnector assembly of an implantable passive fixation lead according tothe present invention. The method involves providing an at least partlyfabricated connector pin made of a first conducting material in step S1.

According to the present invention “at least partly fabricated” means asub-assembly that is either a completely fabricated connector element orat least a partly fabricated raw or start material that can be formedinto a fabricated element. As a consequence, at least partly fabricatedencompasses providing powder, grain, granule or granulate particles ofthe relevant material compacted to a shape from which the final shape ofthe element can be fabricated and formed to a continuous body by sparkplasma sintering. At least partly fabricated also encompasses a finallyfabricated element that is to be connected, such as by spark plasmasintering, to another element of the connector assembly. The expressionalso covers element bodies between these two extremes such as ancontinuous element body of the conducting (in the case of connector pinand connector ring) or non-conducting (in the case of tubular insulator)material that is connected, such as by spark plasma sintering, toanother element of the connector assembly but having a shape differentfrom the final shape of the element. In such a case, the element bodycan be further processed, such as turned, ground, etched, subjected toelectrical discharge machining (EDM), milled, sawed, drawn, tumbled,swaged, forged, welded, following the connection to form the desiredfinal shape and/or surface treatment.

Step S1 can therefore involve, for instance, providing powder particlesof the first conducting material and forming, in a sintering die, theparticles to a desired shape. Alternatively, a fabricated connector pinbody of the first material, such as illustrated in FIG. 4 or 5, isprovided in step S1. Furthermore, the step S1 can involve provided acontinuous body, such as a cylinder or tubular body, of the firstconducting material, where the body has a shape different from the finalshape of the connector pin.

A next step S2 involves concentrically providing an at least partlyfabricated tubular insulator made of a non-conducting material around atleast a portion of the connector pin. This step S2 can, in consistencywith step S1, involve providing powder particles of the non-conductingmaterial and compacting them to a desired shape. Alternatively, afabricated tubular insulator having a shape as illustrated in FIG. 4 or5, but having a longitudinal opening allowing the connector pin to beinserted into the lumen of tubular insulator is provided in step S2 oralternatively a continuous but not finally processed tubular insulatorbody.

Step S3 concentrically provides an at least partly fabricated connectorring made of a second conducting material around at least a portion ofthe tubular insulator. The connector ring can be provided in the form ofparticles of the second material compacted around the body or thecompacted powder of the tubular insulator. Alternatively, the connectorring can be a body having final shape or a partly fabricated continuousbody in which the tubular insulator and the connector pin are threaded.

A next step S4 involves mechanically connecting the tubular insulator tothe connector pin and to the connector ring by spark plasma sintering.Furthermore, in the case any of the providing steps S1 to S3 involvedproviding material particles, the spark plasma sintering operationperformed in step S4 also includes forming a continuous body of thematerial in addition to inter-connecting the connector assemblyelements.

“Spark plasma sintering” or “SPS” is a sintering technique that applies,in addition to pressure, DC current/voltage pulses directly through adie containing a sample to be formed or samples to be inter-connected.The DC current pulses not only pass through the die by also through theactual sample(s) in the case of conductive samples. As a consequence,heat is generated internally through spark discharge between theparticles occurring in the initial stage of the current-voltage pulse.The generation of spark impact pressure, Joule heat and the action ofthe electric field will result in efficient heating, plastic deformationpromotion, high-speed diffusion and material transfer that give anopportunity to conduct low-temperature, short-time sintering ofhard-to-sinter materials and bonding of dissimilar materials.

Spark plasma is formed initially of the sintering process and necksbetween the particles are created. After the initial process, surface,grain-body and volume-diffusion-processes and plastic flow contribute todensification while avoiding coarsening. SPS also facilitates a veryhigh heating or cooling rate (several hundred ° K./minute), hence thesintering process is very fast. SPS is also sometimes denoted fieldassisted sintering technique (FAST) or pulsed electric current sintering(PECS) in the art.

Thus, the expression “spark plasma sintering” as used herein relates toa technique for forming bonds between conducting (metal (alloy)) andnon-conducting (ceramic) material bodies through the application ofpressure and DC current/voltage pulses through the die and the at leastpartly fabricated connector assembly elements of the invention.

FIG. 11 is a schematic a SPS device 500 that can be used according tothe present invention. The device 500 has an upper punch electrode 510connected to an upper punch 530. A corresponding lower punch electrode520 is connected to a lower punch 540. The connector assembly elements560 of the invention to be mechanically connected by SPS according tothe present invention are provided in a sintering (graphite) die 550between the two punches 530, 540. The sample 560 is enclosed togetherwith the punches 530, 540 and the die 550 into a vacuum chamber 590. ADC pulse generator 580 is connected to the upper 510 and lower 530 punchelectrode to thereby apply DC current/voltage pulses over the die 550and through the electrode elements 560. A sintering press 570 isarranged for controlling an exerted pressure applied by the punches 530,540 to the connector elements 560.

FIG. 10 is a corresponding flow diagram illustrating a method ofproducing a proximal connector assembly of an implantable activefixation lead according to the present invention. The method starts instep S10, where an at least partly fabricated connector pin made of afirst conducting material. This step S10 corresponds to step S1 of FIG.9 and is not further described. A next step S11 coats or covers at leasta portion of an outer surface (lateral surface) of the connector pinwith a protective layer. This protective layer is provided to preventthe formation of a mechanical bonding between the connector lead and thetubular insulator. The coating can be applied to only those portions ofthe connector pin that otherwise would come into contact with insulatormaterial in the SPS process. Alternatively, the whole connector pinsurface or at least a major portion thereof can be provided with aprotective coating or layer.

There is a vast amount of materials that can be used as protective layerfor preventing formation of the mechanical bonding. A first example issalt materials, such as sodium chloride (NaCl) or potassium chloride(KCi). In such a case, a thin coating of the salt can be applied to atleast a portion of the outer surface of the connector pin. Theapplication can be in the form of immersing the connector pin in a (highconcentration) saline solution and then evaporating away the solvent.Another possible non-salt, protecting material is graphite.

The main characteristic of this protecting material is that it shouldprevent the insulator from becoming mechanically attached to theconnector pin during the SPS and that the shape of the protective layershould be preserved during the SPS process. Furthermore, the protectingmaterial must be removable after the SPS process, without damaging theconnector element materials. Any materials that fulfill theserequirements can be used according to the invention.

An at least partly fabricated tubular insulator made of a non-conductingmaterial is concentrically provided around at least a portion of thecoated portion of the connector pin in step S12. The discussion inconnection with step S2 of FIG. 9 applies mutatis mutandis to step S12.Step S13 involves concentrically providing an at least partly fabricatedconnector ring made of a second conducting material around at least aportion of the tubular insulator. This step S13 corresponds to step S3of FIG. 9.

The tubular insulator is then mechanically connected to the connectorring by spark plasma sintering in step S14. In addition, if any of theconnector elements were provided in the form of material particles, thespark plasma sintering also forms continuous material bodies having adefined (final or processable) shape. In clear contrast to the sparkplasma sintering step S4 of FIG. 9, the tubular insulator and theconnector pin do not become attached to each other in this step S14 dueto the presence of the protective coating. The coating is removed instep S15 from the outer surface of the connector pin to form a spacingbetween the inner insulator surface and the outer pin surface.

The coating can be removed through different operations, depending onthe particular coating material. If the coating consists of a saltlayer, the connector assembly can be immersed into a solvent, in whichthe salt dissolves. Any remaining salt particles can be rinsed of withfurther solvent, such as water. For non-salt materials, non-aqueoussolvents may be required including organic solvents, such as chloroform,alcohols, etc.

Another possible operation can to oxidize away the protective layertogether with (mild) heating. For example, a graphite layer can beremoved through oxidization at about 400-500° C.

In either case, the coating particle will escape through the (thin)spacings between the short ends of the tubular insulator and theproximal and distal pin portions, respectively.

In an implementation of the invention, the connector pin is provided inthe form of a continuous body of the first conducting material, wherethe body can have the final shape of the connector pin or a more crudeshape from which the final shape can be obtained by further processing.The connector pin material can be made of any of the previouslymentioned material examples, such as stainless steel of medical grade.

The tubular insulator is preferably provided in the form ofnon-conducting material particles that are deposited and compactedaround a portion of the connector pin. The particles can, for instance,be in the form of spark plasma sinterable ceramicgrain/powder/granule/granulate particles, such as A1₂O₃ particles.

The connector ring can then be in the form of a partly fabricated orfinally fabricated body of the second conducting material or in the formof conducting material particles that are deposited and compacted arounda portion of the tubular insulator. The body or particles are preferablymade of the same material as the connector pin, such as stainless steelof medical grade.

In another implementation, also the connector pin is provided in theform of conducting material particles that are deposited and compactedin the sintering die in the form of cylinder, preferably hollowcylinder, or more closely to the final pin shape.

A further implementation uses the three connector elements in the formof continuous bodies of the respective materials.

A test body made of a suitable conducting material of the connector pinand/or connector ring, i.e. platinum, and a preferred non-conductingmaterial of the tubular insulator, i.e. A1₂O₃, have been spark plasmasintered at a temperature of 1175° C. for 5 minute. The test bodies hada diameter of 10 mm and a height of 3 mm and were sintered from A1₂O₃and platinum powder. FIGS. 12A and 12B are scanning electron microscopeimages of the joint between the platinum material 610 and the A1₂O₃material 600 at 500× magnification (FIG. 12A) and 4000× magnification(FIG. 12B). As can be seen from the drawings, spark plasma sintering canbe used for providing a seamless connection between the two differentmaterials 600, 610 without the formation of any cracks or voids in thejoint.

The SPS procedure of the present invention results in a diffusion-basedjoint between the materials. In a small transition zone around thejoint, particles of the materials become inter-mixed to form thediffusion-based, seamless joint.

As is well known in the art, the temperature of the SPS process isdependent on, among others, the particular materials to be sintered andthe thickness of the materials or the size of the material particles.Briefly, the sintering temperature should be below the lowest meltingpoint of the materials to the sintered. Furthermore, the smaller thediameter of the material particles, generally the lower sinteringtemperature can be used. Care must also be taken for materials that aresubject to phase transitions so that not an unaccepted, from mechanicaland/or electrical properties point of view, is formed in the SPSprocess. The pressure that is applied during the SPS process is alsomaterial dependent and depends on the size of the sintered materials.Generally, the pressure per surface area is rather constant for a givenmaterial.

Examples of suitable sintering temperature for some of the materialsuseful according to the invention include ˜1100° C. for A1₂O₃,1000-1100° C. for ZrO₂, 700-500° C. for SiO₂ and hydroxylapatite, <1100°C. for steel.

The optimal SPS sintering parameters can be determined by the personskilled in the art through routine tests and table look-ups regardingthe particular material combinations. The above described parametersettings can be used as starting points in such an optimization process.

It will be understood by a person skilled in the art that variousmodifications and changes may be made to the present invention withoutdeparture from the scope thereof, which is defined by the appendedclaims.

What is claimed is:
 1. A method of producing a proximal connector end ofan implantable passive fixation lead comprising: providing an at leastpartly fabricated connector pin made of a first conducting material;concentrically providing an at least partly fabricated tubular insulatormade of an insulating material around at least a portion of theconnector pin; concentrically providing an at least partly fabricatedconnector ring made of a second conducting material around at least aportion of the tubular insulator; and connecting the tubular insulatorto the connector pin and to the connector ring by spark plasmasintering.
 2. The method according to claim 1, wherein said providingthe tubular insulator and said collectively connecting comprise:concentrically providing powder particles of the insulating materialaround the at least a portion of the connector pin; and spark plasmasintering the powder particles to form the tubular insulatormechanically connected to the connector ring and the connector pin. 3.The method according to claim 1, wherein said providing the connectorring and said collectively connecting comprise: concentrically providingpowder particles of the second conducting material around the at least aportion of the tubular insulator; and spark plasma sintering the powderparticles to form the connector ring mechanically connected to thetubular insulator.